What Are the Parathyroid Glands?

One of the human endocrine glands. The human body has two pairs of parathyroid glands, brown-yellow, shaped like soybeans, which are located in the middle and lower part of the dorsal (or buried in) thyroid gland of the left and right leaves, respectively. Its main function is to secrete parathyroid hormone (PTH) and regulate the metabolism of calcium and phosphorus in the body. Hypoparathyroidism or complete removal (such as accidental removal during thyroidectomy), insufficient PTH secretion causes blood calcium to gradually decrease, while blood phosphorus gradually rises, leading to hypocalcemia convulsions, and even death. PTH and Calcium salts can temporarily relieve symptoms. When hyperparathyroidism and excessive PTH secretion cause bone calcium to enter the blood and strengthen the kidney's reabsorption of calcium, at the same time activate vitamin D3 to become active D3, promote the absorption of calcium in the small intestine, and make blood calcium too high. And inhibit the kidney's reabsorption of phosphate, promote the excretion of phosphorus in the urine, make the blood phosphorus too low, resulting in abnormal deposition of calcium salts in some tissues, pathological calcification of the tissue, and may form kidney stones. Because of the reduction of bone calcium, it is easy to cause fractures. The secretion of PTH is mainly regulated by the concentration of blood calcium. When the blood calcium is high, the PTH secretion decreases, and when the blood calcium is low, the PTH secretion increases. For every 1 mg / dl change in blood calcium, the PTH concentration changes by about 100%. Long-term high or low blood calcium can cause the parathyroid glands to shrink or enlarge (which can be up to 5 times larger). Calcium and phosphorus metabolism in the body is also affected by vitamin D and calcitonin. Calcitonin is secreted by acinar cells in the thyroid and has the opposite effect to PTH.

One of the human endocrine glands. The human body has two pairs of parathyroid glands, brown-yellow, shaped like soybeans, which are located in the middle and lower part of the dorsal (or buried in) thyroid gland of the left and right leaves, respectively. Its main function is to secrete parathyroid hormone (PTH) and regulate the metabolism of calcium and phosphorus in the body. Hypoparathyroidism or complete removal (such as accidental removal during thyroidectomy), insufficient PTH secretion causes blood calcium to gradually decrease, while blood phosphorus gradually rises, leading to hypocalcemia convulsions, and even death. PTH and Calcium salts can temporarily relieve symptoms. When hyperparathyroidism and excessive PTH secretion cause bone calcium to enter the blood and strengthen the kidney's reabsorption of calcium, at the same time activate vitamin D3 to become active D3, promote the absorption of calcium in the small intestine, and make blood calcium too high. And inhibit the kidney's reabsorption of phosphate, promote the excretion of phosphorus in the urine, make the blood phosphorus too low, resulting in abnormal deposition of calcium salts in some tissues, pathological calcification of the tissue, and may form kidney stones. Because of the reduction of bone calcium, it is easy to cause fractures. The secretion of PTH is mainly regulated by the concentration of blood calcium. When the blood calcium is high, the PTH secretion decreases, and when the blood calcium is low, the PTH secretion increases. For every 1 mg / dl change in blood calcium, the PTH concentration changes by about 100%. Long-term high or low blood calcium can cause the parathyroid glands to shrink or enlarge (which can be up to 5 times larger). Calcium and phosphorus metabolism in the body is also affected by vitamin D and calcitonin. Calcitonin is secreted by acinar cells in the thyroid and has the opposite effect to PTH.

Chinese name

Parathyroid glands

Location

Located on the back of the left and right lobes of the thyroid

Number

4

Shape

Flat oval

colour

Brown yellow

Total weight

About 120mg

1 Parathyroid Gland 1, Anatomy of Parathyroid Gland:

There are usually two pairs of parathyroid glands, but they also often have paraglands. They are brownish-yellow and oval in shape, attached to the back of the thyroid gland. Each gland is 3 to 8 mm long, 2 to 5 mm wide, and 0.5 to 2 mm thick. Several glands weigh 0.05-0.3g. The upper pair of glands are in the 1/3 of the dorsal surface of the lateral lobes of the thyroid gland; Parathyroid glands occur from the pharyngeal sac endoderm. The upper pair of glands originate from the fourth pharyngeal sac. The lower pair of glands comes from the third pharyngeal sac, which is very close to the place where the thymus occurs. During the process, it is connected with the thymus and drops together. Generally, it only drops to the lower part of the thyroid gland, and some can reach the thymus. They are mostly located in the thyroid capsule, and some are buried in the thyroid parenchyma. They have a thin layer of connective tissue coating. The capsule sends a septum into the parenchyma, and blood vessels, lymphatic vessels, and nerves pass through the septum to enter. Connective tissue often contains adipocytes, which gradually increase during puberty. It is essentially composed of main cells and eosinophils, and the cells are arranged in clusters or cords with rich capillaries. The main cells secrete parathyroid hormone and regulate calcium metabolism.

2 Parathyroid gland 2, the structure of parathyroid glands:

They are coated with a thin layer of connective tissue. The capsules extend into the parenchyma, and blood vessels, lymphatic vessels, and nerves pass through the septum into the parenchyma. It is essentially composed of main cells and eosinophils. The cells are arranged in cords or clumps with abundant capillaries.

(1) Main cells: This type of cells is the most numerous, with a polygonal shape and a diameter of about 7-10 m. The nucleus is round, with sparse chromatin and light staining, and is located in the center of the cell. The cytoplasm is lightly stained and weakly eosinophilic. When stained with iron hematoxylin or silver immersion, many small particles (probably secretory particles) appeared in the cytoplasm. The main cells are divided into light cells and dark cells according to the differences in the color depth, secreted granules and glycogen content. Bright cells are presumably active cells, and dark cells are resting cells. Under the electron microscope, bright cells had large nuclei, light staining, and light cytoplasm. Golgi complex, rough endoplasmic reticulum and mitochondria are more. There are many round or oval secreted particles with a diameter of about 200 to 400 nm. The secretory granules have a limiting membrane and a dense core, containing parathyroid hormone. Dark cells are smaller, with smaller nuclei and darker cytoplasm. Golgi complex, rough endoplasmic reticulum and mitochondria are fewer, secretory particles are fewer, and there are many lipofuscin particles and glycogen. The main cells have a capillary hole adjacent to one side, and the secreted particles release hormone into the blood from this side. Nerve endings are visible in the perivascular space and on the surface of the main cells, and its exact role is unknown.

(2) Eosinophils: These cells are larger and less numerous than the main cells, and are often located individually or in groups between the main cells. The cells are polygonal or irregular, with small nuclei and deep staining, and the cytoplasm is strongly eosinophilic. The main feature of the ultrastructure is that there are a large number of dense elongated mitochondria, and they are numerous. There are many glycogen particles between the mitochondria. The Golgi complex is small and the endoplasmic reticulum is sparse. There are few secretory particles. The strong eosinophilicity of the cytoplasm is caused by dense mitochondria. The significance of such cells is unknown, not before puberty, and gradually increasing since then. See also some transitional cells between main cells and eosinophils. These cells contain mitochondria and glycogen, which also contain secreted particles. During parathyroid hyperplasia, transitional cells increase, and watery clear cells often appear. These cells contain a lot of glycogen and very few mitochondria and endoplasmic reticulum. During routine staining, the cytoplasm is clear as water because the glycogen in the cells is dissolved. In recent years, studies have shown that the parathyroid glands only have main cells, and other types of cells have different performances and some have degenerative changes.

3 Functions of Parathyroid Gland 3, Parathyroid Gland:

This gland is necessary for life. The main cells secrete parathyroid hormone and regulate blood calcium content. Animal experiments show that if this gland is completely removed, the blood calcium content will drop sharply, and the muscles will spasm and cause death. Parathyroid hormone regulates the metabolism of calcium and phosphorus. Its secretion is mainly regulated by blood calcium levels, and is not directly affected by other endocrine glands and nerves. When the blood calcium is reduced, this gland stimulates the secretion of hormones, which act on bone cells and osteoclasts, and promote the absorption of calcium in the bone and release it into the blood. When blood calcium increases, this hormone is inhibited. This hormone also causes the kidneys to excrete phosphorus, which reduces blood phosphorus. It also promotes calcium absorption in the gastrointestinal tract. When hyperparathyroidism is increased, blood phosphorus is reduced and calcium is increased, and calcium salts of bone are overabsorbed, causing osteoporosis; at the same time, calcium salts are deposited in other organs. When hypoparathyroidism is impaired, blood phosphorus increases and calcium decreases, and bone becomes dense and overcalcified.